Implantable heart stimulator

Abstract

An implantable heart stimulator has an AV-interval generator which generates a variable AV-interval and which is provided with a predetermined basic AV-interval. The heart stimulator has a counter that counts the number of times the AV-interval is changed in response to a fusion avoidance algorithm or a stimulation threshold search algorithm during a predetermined time period. The basic AV-interval is changed if the number of times counted by the counter is greater than a predetermined value.

1. An implantable heart stimulator comprising an AV-interval generator which generates a variable AV-interval and which is provided with a predetermined basic AV-interval, and a counter that counts a number of times the AV-interval is changed during a predetermined time period, said counter generating and applying an output signal to said AV-interval generator to cause said AV0-interval generator to change said basic AV-interval if said number of times is greater than a predetermined value. 
   
   
     2. A heart stimulator according to  claim 1  wherein said AV-interval generator changes the basic AV-interval by an amount in a range of −30 to 30 milliseconds. 
   
   
     3. A heart stimulator according to  claim 2  wherein said AV-interval generator changes the basic AV-interval by −20 ms or +20 ms. 
   
   
     4. A heart stimulator according to  claim 1  wherein said predetermined value is in a range of 2-10. 
   
   
     5. A heart stimulator according to  claim 1  wherein said predetermined time period is between 1 and 3 minutes. 
   
   
     6. A heart stimulator according to  claim 1  further comprising a control unit provided with a fusion avoidance algorithm. 
   
   
     7. A heart stimulator according to  claim 6  wherein said fusion avoidance algorithm, when activated, makes the AV-interval generator temporarily prolong the AV-interval. 
   
   
     8. A heart stimulator according to  claim 1  further comprising a control unit provided with a stimulation threshold search algorithm. 
   
   
     9. A heart stimulator according to  claim 8  wherein said stimulation threshold search algorithm, when activated, makes the AV-interval generator temporarily shorten the AV-interval.